Ask a Vet: How Can People With Compromised Immune Systems Live Safely With Cats?


Over my years as a veterinarian the topic of pets living with immune-compromised people has come up repeatedly both in my practice and online. Some of the stories have been very nearly tragic.

For instance, when I was a new veterinary graduate working at a new job in San Francisco, I encountered a very depressed gentleman. He was HIV positive, and had been told by his doctor that for health reasons he couldn’t keep his dogs. He came to my office to put the dogs to sleep, and he announced that his intention was to go home and commit suicide once the act was done. I did not know the man, and at that time I was not very well versed in the controversy that once surrounded cohabitation between immune-compromised people and pets. But I knew I wasn’t going to help this man with his stated goal in any way.

Fortunately, my job was at a small practice that had been a part of the neighborhood for decades. My boss knew the man’s next door neighbor, and in what was no doubt a violation of privacy standards, my boss called the neighbor to explain the situation. After I politely refused to euthanize the dogs and spent the rest of the appointment consoling the man (who had many reasons to be depressed) and urging him to seek professional help, he went home and was greeted by his neighbor who helped to prevent him from doing anything rash. In the end the dogs and the man lived, and a better doctor was found for him.

Fortunately such outrageous stories now are almost unthinkable. The myriad emotional and physical benefits of pets are now so well respected by the medical establishment that pet therapy is a much more accepted subject than pet relinquishment. The question that now looms is not whether immune-compromised individuals can live safely with pets, but how can immune-compromised people safely live with pets.

This issue was brought up recently on my Facebook page (which, by the way, is the best way to connect with me — feel free to like the page while you’re there). A reader named Adrianna had a question about litter box cleaning for people with vasculitis. Here’s an excerpt:

My Facebook friends and I have been debating the merits and demerits of washing a rinsed cat litter box through a dishwasher. We all have some form of vasculitis and are immunosuppressed. I think at the heart of the debate is how can we the immunosuppressed live safely with our beloved pets. I know many people would love to read an article on this, as so many people are immunosuppressed, not just vasculitis patients.

First, a disclaimer. Although many vets are taught more about zoonoses (diseases shared by animals and humans) than many physicians, I must be clear that a veterinarian can never offer definitive answers about human health. I therefore must emphasize that all immune-compromised people should seek the counsel of a competent physician in these matters. What follows is general information related to living safely with pets, but it should not be directly applied to any person’s individual circumstances.

Although no veterinarian can ever be a definitive authority on human health, the Center for Disease Control and Prevention (CDC) can and is. They have a special website dedicated to living safely with pets called Healthy Pets Healthy People. That website contains a link for people at extra risk — such as those with compromised immune systems. I strongly urge any person with a compromised immune system to read the site thoroughly. You will note that nowhere on the site does it say that immune-compromised people can’t have pets.

Here’s what it all boils down to: It is generally safe for people with compromised immune systems to live with pets as long as the pets are healthy and as long as basic hygiene rules are followed.

Keeping your cat healthy

The best way to avoid catching a pathogen from your cat is to keep your cat free of pathogens. There are several basic steps that all people — not just immune-compromised ones — should follow.

  • Keep your cat indoors. Outdoor cats may hunt, which can lead to exposure to pathogenic bacteria such as Salmonella, Campylobacter, and E. coli as well as zoonotic parasites such as roundworms and Toxoplasma gondii. Outdoor cats also may get into fights and come home with bacteria-filled abscesses.
  • Use regular flea prevention. Fleas are vectors for a number of zoonotic diseases such as bartonellosis (also known as cat scratch fever) that are shared by cats and people. Flea feces also poses a significant environmental contamination risk.
  • Use a regular broad spectrum anti-parasite (deworming) medication. These medications protect your cat against heartworm disease; they protect both you and your cat from intestinal worms.
  • Get regular semiannual (at least) veterinary checkups for your cat, and follow all of your vet’s recommendations.
  • Keep your cat’s nails trimmed. Even accidental cat scratches can cause infections.
  • Avoid raw diets. I am not trying to turn this into a raw food debate, and this item is a likely exception to the “all people” reference above since many people with healthy immune systems can attest that they have come to no harm from feeding raw diets to their cats. It is also true that cooked food can be contaminated with bacteria after the cooking is done, so feeding cooked food provides no guarantee that you won’t catch Salmonella from your cat. However, it is a fact that cooking kills bacteria (such as Salmonella), roundworms, and Toxoplasma. People with compromised immune systems are at extra risk from these pathogens, and they should not feed raw diets.

Proper hygiene

Here is where I will weigh in on Adrianna’s dishwasher question. One of the most basic principles for living safely with cats is this: The litter box should never enter the kitchen or dining room. Most of the serious zoonotic feline pathogens spread from cats to humans by way of fecal-to-oral contact. Having the litter box, which is a receptacle for feces, anywhere near food preparation or consumption areas is a big no-no. Adrianna, a dishwasher is a great way to sanitize a litter box as long as it is purposefully installed in an area away from the kitchen and never used for anything other than cleaning litter boxes. I strongly urge against washing dishes in any dishwasher that is used for litter boxes since complete sterilization during and between cycles cannot be guaranteed. And don’t wash a litter box in a kitchen dishwasher.

Here are some more tips:

  • The litter box is by far the most likely source of feline-to-human pathogen transmission. It should be kept very clean so that cats are less likely to step in feces and spread bacteria around the house. It should be cleaned by a person with a non-compromised immune system if possible. If that is not possible, then I recommend wearing gloves and a surgical mask while cleaning the box. Use a new mask each time (otherwise the mask will simply serve as a bacterial culture medium). Thoroughly wash your hands after cleaning the box. The box can be sterilized with boiling water and soap (according to the CDC), but it’s best to have a person with a non-compromised immune system (or a single-purpose dishwasher) do this.
  • Make sure your cat stays clean. If your cat can’t groom himself properly, have him groomed regularly. Groomers and veterinarians can perform “sanitary clips” (sometimes colloquially referred to as “kitty Brazilian waxes”) to keep the hindquarters clean.
  • Keep the toilet lid closed, to keep cats from drinking water that is potentially contaminated with bacteria.

The special case of toxoplasmosis

Toxoplasma gondii is a microscopic parasite whose definitive host is cats. It poses a significant health threat to pregnant women and people with compromised immune systems. Although much ballyhoo is made about this organism, people should be aware that cats are capable of shedding the organism for only a few days of their lives. Human exposure is more likely to occur from eating uncooked vegetables that are contaminated by feral cats than from household pets. This is especially true for adult house cats who live only indoors and eat cooked food.

With that said, cat owners should be aware that their pet might shed this organism at some point. It is shed through the feces and the litter box tips provided above generally will keep people with compromised immune systems safe. T. gondii presents a special case for litter boxes to be cleansed daily — the oocysts (eggs) shed by cats generally are not infective for at least a day, so daily cleaning is likely to clear out the parasites before they can infect a person.

Much more information about T. gondii can be found here.

The above recommendations are presented as general information only. As I mentioned, cat owners should always follow the advice of a knowledgeable physician and should familiarize themselves with the information available from the CDC. But with that said, I will say that because of the many health benefits that cats offer, it my belief that people with compromised immune systems not only can live safely with cats, but also can live more healthily with them than without them.

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